Mid-ocean ridge:the longest chain of mountains in the world. Sonar:a device that bounces sound waves off underwater objects and then records the echoes of the waves. Sea-floorspreading:the process that continually adds new material to the ocean floor. Deep-ocean trenches:deep underwater canyons. Subduction:the process by which the ocean floor sinks beneath a deep-ocean trench.
Outline
Mapping the Mid-Ocean Ridge
Sonar maps sea-floor ridge
most mountains in the sea-floor are usually hidden under hundreds of meters of water.
The island of Iceland is an example of a mid-ocean-ridge
Evidence for Sea Floor spreading
Evidence from molten material
Scientist found strange rocks that looked like toothpaste squeezed from a tube,on the sea floor
Such rocks can only be found when molten material hardens quickly after erupting under water.
Evidence from magnetic stripes
Scientists discovered that rock that makes up the ocean floor lies in a pattern of magnetic stripes
Evidence from drilling samples
Samples from the sea floor were brought through pipes of a drilling ship. They found that further away from the
ridge the samples were taken, the older the rocks were.The youngest rocks were always in the center of the ridges.
Deep ocean trenches
A deep-ocean trench forms where oceanic crust bends downward.
Subduction takes place in deep-ocean trenches.
At deep-ocean trenches, subduction allows part of the ocean floor to sink back to the mantle, over tens of millions of years
Subduction and Earth's oceans
The process of subduction and sea-floor spreading can change the size and shape of the oceans.
Subduction in the pacific ocean
The pacific ocean is shrinking, because the deep-ocean trench has swallowed more oceanic crust than the mid-ocean ridge can make.
Subduction in the Atlantic Ocean
The Atlantic Ocean is expanding because it only has a few short trenches. The spreading sea floor moves the continents,
Table of Contents
Chapter 1.4
Vocabulary
Mid-ocean ridge:the longest chain of mountains in the world.
Sonar:a device that bounces sound waves off underwater objects and then records the echoes of the waves.
Sea-floor spreading:the process that continually adds new material to the ocean floor.
Deep-ocean trenches:deep underwater canyons.
Subduction:the process by which the ocean floor sinks beneath a deep-ocean trench.
Outline
Mapping the Mid-Ocean Ridge
Evidence for Sea Floor spreading
Scientist found strange rocks that looked like toothpaste squeezed from a tube,on the sea floor
Evidence from magnetic stripes
Samples from the sea floor were brought through pipes of a drilling ship. They found that further away from the
ridge the samples were taken, the older the rocks were.The youngest rocks were always in the center of the ridges.
Deep ocean trenches
Subduction and Earth's oceans
- The process of subduction and sea-floor spreading can change the size and shape of the oceans.
- Subduction in the pacific ocean
- The pacific ocean is shrinking, because the deep-ocean trench has swallowed more oceanic crust than the mid-ocean ridge can make.
- Subduction in the Atlantic Ocean
back to KHAY homepage- The Atlantic Ocean is expanding because it only has a few short trenches. The spreading sea floor moves the continents,
>> and the ocean gets wider.